Touch panels are used to input, to cell phones or personal computers, texts or images besides operational commands. Touch panels perform signal processing for converting a sensed touch of a finger or a stylus pen into an electric signal.
Some stylus pens equipped with electronic circuits may perform not only a function of simple touch input but also a function of a mouse such as selecting or dragging a part of an image by generating an electric signal.
When a stylus pen is equipped with an electronic circuit as described above, power is required for operating the electronic circuit of the stylus pen. A stylus pen may be further equipped with a battery for supplying power thereto. However, recently, a body of a cell phone is provided with a dedicated panel for supplying power so that the power supply panel may wirelessly supply power to a stylus pen. Such a wireless power supply technology is disclosed in Patent Document 1.
(Patent Document 1) JP4866941 B
Patent Document 1 discloses a power supply technology in which power is transferred to a coil of a stylus pen by an induction coil of a power transmission device 4 disposed under an LCD module 3 in a smartphone, as illustrated in FIG. 1. For reference, FIG. 1 exemplarily illustrates a smartphone including an external protective cover 1, a touch panel 2 disposed under the protective cover 1, the LCD module 3 disposed under the touch panel 2, the power transmission device 4 disposed under the LCD module 3 to transfer power by the induction coil, and a frame 5 forming an outer shape of the smartphone.
Although described in embodiments of the present disclosure, the protective cover 1 may not be an essential element since the protective cover 1 is integrated with the touch panel 2 according to a recent trend.
A position detecting device such as a smartphone includes an additional circuit disposed under an LCD module in order to supply power to a stylus pen, but such an additional circuit panel for supplying power causes an increase in cost. Furthermore, it causes an increase in the thickness of a cell phone, degrading a commercial value thereof.
In particular, the wireless power supply technology disclosed in Patent Document 1 is described below.
A resonance induction circuit installed at a power transmission side (power transmission device) converts power energy into electromagnetic energy and radiates it as electromagnetic waves into space.
A power reception side (stylus pen) receives the electromagnetic energy through a resonance induction circuit installed at the power reception side. Here, there is a condition of electromagnetic coupling or inductance coupling between an inductance component of a coil of the power transmission side and an inductance component of a coil of the power reception side.